The present invention relates generally to process cartridges for electrophotographic image forming, and more particularly relates to increasing the bias force between photosensitive members and developers in such cartridges.
A process cartridge used for the formation of electrophotographic images in devices such as printers, fax machines, word processors and photocopiers contains a photosensitive member and a developer. The developer carries toner by electrostatic and/or magnetic force to the photosensitive member and is specifically spaced from the photosensitive member such that toner will migrate from the developer to the photosensitive member by the force. The spacing between the developer and the photosensitive member must remain constant throughout the life of the cartridge so as to avoid varying the mass of toner transferred. By maintaining a steady mass of toner transferred between the developer and the photosensitive member, the print quality is improved. This spacing is generally controlled by a gap spacer or spacers located on the photosensitive member, the developer, or both.
A process cartridge generally consists of two halves swingably opposed to each other such that the spacers on the photosensitive member and/or the developer are in intimate contact with their opposing members but are not locked into position. The two swingably opposed halves may have slight rotational and/or translational movement with respect to each other. The halves are generally referred to as the cleaner half and the developer half The cleaner half contains the photosensitive member, and it also generally contains a photosensitive member cleaning system and a photosensitive member charging system. The developer half contains the developer and also generally contains the toner reservoir which supplies the developer with toner.
To maintain contact between the spacers and their opposing members, a bias force of some type is required. This bias force may come from the toner hopper mass, springs, or a combination thereof. In process cartridges relying on the toner hopper mass to maintain all or part of the bias force between the spacers and their opposing embers, the force decreases over time because the weight of the developer half decreases. In this condition, any movement of the developer half with respect to the cleaner half will influence the spacing between the photosensitive member and developer and, thus, influence print quality. Such a movement might arise from various sources such as misshapen photosensitive member gears, misshapen developer gears, uneven assembly of developer and/or photosensitive member gears, incorrect tolerances of components, low quality of components, dirt and debris, vibration, paper feed, alterations in the drive torque of the system, a twist of the system, or combinations of these and other sources of external or internal force.
These problems may be increased when used process cartridges are remanufactured for reuse and old components are replaced with new components that may not be designed or manufactured to the same specifications as the original components. Thus, both in original and remanufactured electrophotographic process cartridges, there exists a need for an improved means of maintaining a bias force to maintain a constant spacing between developers and photosensitive members.
In accordance with one aspect of the present invention, there is provided a method and apparatus for increasing the bias force between a cleaner half and a developer half of a process cartridge.
In one embodiment of the present invention, the bias force between a cleaner half and a developer half of a process cartridge is increased by placing shims adjacent to one or both ends of bias springs within a process cartridge.
In another embodiment of the present invention, bias springs having a high spring constant are used to increase the bias force between a cleaner half and a developer half of a process cartridge.
In another embodiment of the present invention, an external bias force is supplied between the two halves of the process cartridge either in addition to or instead of a bias force supplied from inside the cartridge. In one embodiment, springs are placed externally on the cleaner half, developer half, or both halves. In another embodiment, static weights are placed inside and/or outside the developer half and/or the cleaner half.
In another embodiment of the present invention, a bias force between the cleaner half and the developer half of a process cartridge is increased by mounting one or more elastic members on the cleaner half or developer half. In this embodiment, the elastic member or members abut either the cleaner half, the developer half or both halves and a printing apparatus so as to increase the bias force between the halves.